MYOSTATIN (GDF-8)

Interindividual differences in muscle mass are due to environmental factors but also for a large part due to genetic determination. Earlier studies provide heritability estimates > 75%. Identifying a gene for muscle mass might also be a causative gene for maximal musclular strength due to the moderate to high correlation between these two traits. Results from animal studies show that myostatin (GDF-8) is an important regulator of muscle development. The high degree of myostatin sequence conservation in non-human species led to this study to see whether GDF-8 is also responsible for a part of the interindividual differences in muscle mass in humans. PURPOSE: To test whether myostatin is associated with muscle mass in a human case-control study. METHODS: An extended set of anthropometrical measurements was taken from 50 male power athletes (29.8 ± 8.8 years) and 57 control subjects (22.4 ± 3.7 years), not selected for muscularity. Muscle mass was determined by circumference measures corrected by skinfolds. Using mathematical formulas muscle mass of am and leg was calculated. Four recently described polymorphic sites in the myostatin gene were genotyped: Ala 55, Lys 193, Glut 164 and Pro 198. RESULTS: There appeared to be no evidence for allele frequency differences in the four studied polymorphisms in the myostatin gene between the two groups, indicating that variation in muscle hypertrophy is not associated with variation at the myostatin locus. Also myostatin sequence variation within groups was sparse. Only two individuals, one in the control and one in the power athlete group, were heterozygous for K153R. Their extremity muscle mass indicators as well as somatotype components did not indicate a specific extreme phenotypic profile in both K153R heterozygotes. CONCLUSION: The lack of a significant relationship between myostatin genotypes and overall muscle mass might suggest that muscularity is not significantly influenced by genetic variation at the myostatin locus.